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Existing and new foundation

Existing and new foundation

Existing and new foundation

(OP)
Hi
Please find this thread
https://www.eng-tips.com/viewthread.cfm?qid=441767...
The discussion ended with the new and existing foundation concerns.
If the new foundation for the proposed steel frame is at the same level with the existing single column foundation, and the two foundations interfere, using adhesive anchors (on sides) what are the concerns?
My thought is that the adhesive anchors could help in resisting differential settlement between the two interfered foundations by shear.
How the reduced area of the new foundation (due to interference with the existing foundation) is solved?

RE: Existing and new foundation

Quote (hoshang)

My thought is that the adhesive anchors could help in resisting differential settlement between the two interfered foundations by shear.

Don't do that. Say the anchors do prevent differential settlement (highly unlikely). Now the new slab is no longer supported by soil, it is suspended in "mid-air" (a very small distance above the soil).

1) Is the new slab going to be designed exactly the same as an elevated slab? (That's what it has become).

2) With the new slab now "elevated", much of new slab's dead and live load will have to be supported by soil under the existing slab. Will this increased load on soil under the exiting slab cause the existing slab to settle?

Differential settlement is managed (not necessarily prevented) by proper attention to the supporting soil, not by structural "tricks".

www.SlideRuleEra.net idea
www.VacuumTubeEra.net r2d2

RE: Existing and new foundation

(OP)

Quote (SlideRuleEra)

Please find the link:
https://www.screencast.com/t/MbOvBBN3bFy
The existing column and foundation are drawn in blue. The new beam and column are drawn in red. The new foundation is drawn in green.
I can't remove the existing column and foundation before the new foundation and steel frame is completed. So while constructing the new foundation, it will interfere with the existing foundation.

Quote (hoshang)

How the reduced area of the new foundation (due to interference with the existing foundation) is solved?

Quote (hoshang)

My thought is that the adhesive anchors could help in resisting differential settlement between the two interfered foundations (by shear).

RE: Existing and new foundation

hoshang - A foundation does not have to be a rectangle, such as you have shown in green. It can be another shape, but the shape has to be carefully sized so the load on it has little or no eccentricity. Work with a geotechnical engineer to get a shape that is acceptable.

www.SlideRuleEra.net idea
www.VacuumTubeEra.net r2d2

RE: Existing and new foundation

(OP)

Quote (SlideRuleEra)

A foundation does not have to be a rectangle
Thanks
Please find the link.
I recalculated and the dimensions of the new footing resulted in a square shape (3.05x3.05x0.5)m.
First I thought you meant trapezoidal footing, but trapezoidal didn't solve the problem. So I tried putting the column on one corner of the square footing. I appreciate any thought it may arise.
https://www.screencast.com/t/6YRBeDSdK

RE: Existing and new foundation

hoshang - If the loading on the new footing is from the new columns, like shown below, none of the footings proposed will work correctly. The load has too much eccentricity:



If my sketch is correct, a "strap footing" should work. The strap footing would be like the drawing below, except that both columns will like the "eccentrically loaded column footing" in the drawing.





Your plan may look something like this:

www.SlideRuleEra.net idea
www.VacuumTubeEra.net r2d2

RE: Existing and new foundation

(OP)

Quote (SlideRuleEra)

If my sketch is correct, a "strap footing" should work
Thanks. A strap footing is the solutions. Bowel states that in such cases of mine strap footing "must" be used.

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